For my 2007? I am sick of looking at shitty websites that are slow to load and just list every part on the back door but won't show me a diagram. Partsouq only shows the whole switch part number 84945 and to refer to figure 84-20 which I don't find anywhere. There are a bunch of parts like rear handle outer seal which makes me thing the boot would have been an available part at some point. That boot has gotten sticky now and makes my fingers black when I open it. I tried putting some wurth's on it but it made it worse.
I do not know the part number but Google and Amazon both have plenty as does eBay . I've ordered a few fakes work quite well .
I have four cars and work.on for folks . I've not had to replace a replacement yet. Usually folks blow up cars . Need batteries or actuators . Not doing that etc.
Because the one Toyota installed on your car has worked out so well? Every 2007 I've owned or worked on had the gummy rubber. Like Tom, I've done many of these. The inexpensive ebay kits work perfect. I keep a couple handy. You really want to put some effort into cleaning the button first to remove all the gummy rubber from Toyota's F-up. I remove the garnish and button, use a small pick and AutoZone brake cleaner on a rag to get it like new before installing the new rubber boot. Many people just clean the goo off and leave it like that.
The official part number appears to be 84840-47020 if your Prius has smart entry or it's 84840-47010 w/o smart entry. It doesn't appear Toyota sells just the rubber cover. Like other suggestions, they sell aftermarket replacement rubber cover on Amazon and Aliexpress.